Food service tray

ABSTRACT

A food service tray which allows selective heating and/or cooling of meal components carried thereby. A base member of a thermally insulating material has a plurality of compartments divided into serially connected flow chambers having inlet and outlet openings. Food receptacles made of a thermally conductive material carry the meal components and are inserted into the compartments. Thermally insulating lids then cover the food receptacles. A refrigerated fluid under pressure may be passed through all or part of the flow chambers to thereby maintain the contents of the food receptacles therein in a chilled condition. A heated fluid under pressure can then be passed through selected flow chambers to thereby rethermalize or heat the contents of the food receptacles in the heated flow chambers to a proper serving temperature. Simultaneously with the heating of some food receptacles, the flow of refrigerated fluid can be continued to other flow chambers to maintain other meal components in a chilled condition for serving.

This is a Division, of application Ser. No. 480,946, filed June 19, 1974now U.S. Pat. No. 3,952,794 issued Apr. 27, 1976.

BACKGROUND OF THE INVENTION

This invention generally relates to food service trays. Morespecifically, this invention relates to a food service tray carryingvarious meal components, all of which may be kept chilled until shortlybefore serving. Most particularly, this invention relates to a foodservice tray which allows selective rethermalization of certain mealcomponents while other meal components are kept chilled.

The need for a food service system which would allow preparation ofmeals long before they are needed, hold the meals at a safe temperature,and then reheat portions of the meals for serving has been wellrecognized. Hospitals in particular need such a system. The prior artshows many attempts to develop such systems. However, these systems allhad flaws in either workability or expense. For example, infra-red lampshave been used to reheat portions of meals. Microwaves have also beenused for heating selected portions of an entire meal. The so-called "hotpellet" system is also used. In such a system, a large mass of heatedmaterial is placed under a tray to keep the contents of the tray warm.However, the heated material could be spilled if the tray wereoverturned leading to a possible burn hazard. In some cases, a pluralityof pre-prepared meals have been transported and stored in totallyenclosed, refrigerated carts. In some cases, the service tray or foodcontainers were quite expensive in order to perform specialized heatingor cooling function; this required reuse of these components because ofeconomic factors. Ideally, however, all of the food service componentsshould be disposable, with the exception of a transport cart or carrier.I have found that the objectives of good thermal control of mealelements and disposability of the service components can be achieved byforming a base member of an insulating material and providing in thebase member compartments divided into two flow chambers. Then, thermallyconductive receptacles carrying meal elements are inserted in thecompartments and covered with an insulating lid. Chilled air may becirculated through the flow chambers to keep all of the meal elementschilled. If some elements are to be served heated, heated air may beselectively circulated through selected flow chambers to re-heat or keephot these particular meal elements.

SUMMARY OF THE INVENTION

My invention is a food service tray and a method for using it. A basemember of the tray is made of a thermally insulating material andincludes a plurality of compartments having upstanding wall portionsopen at their upper ends. Each compartment has located therein a meansfor dividing the compartment into two substantially isolated, seriallyconnected flow chambers. There is further provided a fluid inlet openingin one of the flow chambers and a fluid outlet opening in the other flowchamber. A plurality of food receptacles, made of a thermally conductivematerial, are engaged in the plurality of compartments. The tray iscompleted by thermally insulated lid means for covering the plurality offood receptacles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the base member of the presentinvention;

FIG. 2 is a perspective view of the base member of the present inventionwith food receptacles inserted into the open compartments;

FIG. 3 is a perspective view of the complete food service tray of thepresent invention;

FIG. 4 is a cross-sectional, elevational view taken generally along theline 4--4 in FIG. 3;

FIG. 5 is a schematic perspective view of a cooling and/or heatingsystem useable with the food service tray of the present invention; and

FIG. 6 is a time versus temperature chart illustrating how the foodservice tray of the present invention allows reheating some mealcomponents while other meal components are retained in a chilledcondition.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a base member 10 which is one component of the foodservice tray of the present invention. The base member 10 includescompartments generally designated as 12 and 14. The compartments 12 and14 include upstanding wall portions 16 and 16a respectively which areopened at their upper ends. The compartments 12 and 14 also includebottom portions 18 and 18a which are connected to the wall portions 16and 16a. A spline portion 20 extends through substantially the entirecompartment 12. A similar spline portion 22 extends throughsubstantially the entire compartment 14. An opening 24 is formedcompletely through one upstanding wall portion 16 of the compartment 12on one side of the spline 20. A second opening 25 extends completelythrough the wall portion 16 on the opposite side of the spline 20.Corresponding openings 28 and 29 are similarly formed in the wallportion 16a of the compartment 14. As will be explained later in detail,one of the openings 24 or 25 is a fluid inlet opening and the other ofthe openings 24 or 25 is a fluid outlet opening. Similarly, the openings28 and 29 define one fluid inlet opening and one fluid outlet opening.The spline portions 20 and 22 divide the compartments 12 and 14 into twodistinct portions. It is obvious from FIG. 1 that spline portions 20 and22 do not extend upward the entire upward extent of the wall portions 16and 16a. However, as will be more obvious with respect to FIG. 4, thespline portions 20 and 22 serve to define two substantially isolatedflow chambers within the compartments 12 and 14. The base member 10 mayalso include a depression 30 for a beverage container and a seconddepression 32 which may be used to contain silverware, napkins orcondiments for use with the meal to be served using the food servicetray of the present invention. For ease of handling and storage, thebase member 10 also includes a flange portion 34 which extends aroundthe entire periphery of the base member 10. In addition, thecompartments 12 and 14 may be further defined from the flange portion 34by an upstanding rib portion 36 which extends around the perimeter ofthe compartments 12 and 14 and is spaced slightly outwardly from theedge of the compartments 12 and 14. The rib 36 serves, as best seen withrespect to FIG. 2, to retain food receptacles that are placed into thecompartments 12 and 14. The base member 10 is preferably formed as anintegral assembly from a material which has a low thermal conductivityvalue. That is, the base member 10 should be formed of a material whichis a good thermal insulator. A material that has been found particularlyeffective for this purpose is a polystyrene foam material having athermal conductivity value of 0.000083 gm cal/cm² sec° C/cm and whichhas a thickness of from 1.5 to 4.0 mm. The base member 10 may be formedin any convenient manner, for example thermoformed from sheet materialor molded in a steam chest from expandable beads of material.

In FIG. 2, a plurality of food receptacles 38, 39, 40 and 41 have beeninserted into the compartments 12 and 14. The receptacles 38 and 39 havebeen placed into the compartment 12 and the receptacles 40 and 41 havebeen placed into the compartment 14. The food receptacles 38 through 41are designed to carry the individual constituents of a meal that is tobe served. By dividing the constituents of the meal into thosecomponents which are to be served heated and those which are to beserved in a cooled or chilled condition, it is possible to make use ofthe division of the compartments 12 and 14 and their separation. Thefood receptacles 38 through 41 illustrated in FIG. 2 are allsubstantially identical, and a detailed description of one of thesereceptacles would serve for all. For example, the food receptacle 38 ismade up of upstanding wall portions 42 which are joined to an integralbottom portion 44, and is open at its upper end. In addition, a supportflange 46 is connected to the upstanding wall portions 42 at their upperends and extends outwardly therefrom. The support flange 46 rests onadjacent portions of the flange portion 34 of the base member 10. It isreadily apparent in FIG. 2 that the rib 36 is provided to prevent thefood receptacles 38 through 41 from shifting in position once they havebeen inserted into their respective compartments 12 or 14. The rib 36will engage with the support flange 46 and prevent it from shifting. Itshould be recognized that while the shape of the food receptacles 38through 41, as shown in FIG. 2, is of a generally rectangular or squareconfiguration, the precise shape of the food receptacles is not acritical factor in proper operation of the entire food service system.The receptacles may be of any convenient shape, and, in fact, thecompartments 12 and 14 could be similarly revised in shape to conform toa desired configuration of a food receptacle. What is required is thatany compartment used must contain a means for dividing the compartmentinto two substantially separated flow chambers that are seriallyconnected. The primary characteristic of the food receptacles 38 through41 is that they must be made of a material which allows good transfer ofheat or a material which has a relatively high thermal diffusivityvalue. A material that has been found satisfactory is polystyrene havinga thermal conductivity value of 0.00019 gm cal/cm² sec°C/cm and having athickness of 0.6 mm. or less. Receptacles of the type illustrated andhaving the required characteristics can be readily produced in aone-piece, seamless configuration from sheet-like polystyrene byconventional thermoforming techniques. Of course, mechanical strengthconsiderations enter into the decision as to the thickness of thematerial to be used. For example, satisfactory material could be thingauge aluminum, polypropylene, polyethylene, molded pulp or polysulfonewhich is formed into the shape of the food receptacle that is desired.

In FIG. 3, the entire food service tray, generally designated as 50, ofthe present invention is shown. The food service tray 50 is completed byplacing lids 52 through 55 over the food receptacles 38 through 41. Theprecise configuration of the lids 52 through 55 is not critical but theyshould be of a dimension such that they will fit over the foodreceptacles 38 through 41 relatively tightly to insulate the contents ofthe food receptacles 38 through 41 from the outside atmosphere. In fact,it would be possible to use one elongated lid to replace the lids 52 and53 and the lids 54 and 55. Again, keep in mind that the precise shape ofthe food receptacles 38 through 41 may be varied and of course the shapeof the lids therefor would also be varied to conform to the specificconfiguration chosen. The main consideration with respect to the lids 52through 55 is that they be thermally insulating. The lids 52 through 55may preferably be made of the same material as that which forms the base10. In the configuration shown in FIG. 3, a meal could be placed intothe food receptacles 38 through 41 and with the lids 52 through 55 inplace maintained at the temperature at which the components of the mealwere inserted for a reasonable period of time simply because of thethermally insulating properties of the base 10 and the lids 52 through55. However, this particular food service tray is designed to allowassembly of entire meals a considerable time before the service of ameal is desired and maintain the components of the meal in a cooled and,therefore, preserved condition until a short period prior to the serviceof the meal. At that time, the hot portions of the meal will bere-thermalized while the portions of the meal to be served chilled willbe maintained in their chilled condition.

FIGS. 4 and 5 illustrate precisely how this rethermalization combinedwith storage function may be performed. As particularly seen in FIG. 4,one of the food receptacles, in this case food receptacle 38, is seen tobe so proportioned that it is generally in contact with the top of thespline 20. It is not critical that this contact be maintained in allcases, but for most efficient operation of the entire food service tray50 this is a desirable situation. Note now that with the food receptacle38 in contact with the spline 20, the openings 24 and 25 do indeed openinto two substantially separated compartments or flow chambers definedby the spline 20. The spline 20, as clearly shown in FIG. 1, terminatesshort of the wall opposite the inlet openings 24 and 25 and thus allowsflow of a fluid through the two chambers so defined. FIG. 5 illustratesin a somewhat schematic form precisely how this might be accomplished.Note that in FIG. 5 the food receptacles 38, 39, 40 and 41 and theirassociated lids 52, 53, 54 and 55 have been omitted for clarity. Ofcourse, these elements would normally be present. First of all, there isa means for supplying a flow of refrigerated fluid under pressure to thetray 50. By way of example, this means may include a refrigeration unit56 having associated therewith a blower 57. The refrigeration unit 56 isused to chill air which is blown therethrough from the blower 57. Carbondioxide from dry ice or nitrogen from liquid nitrogen could also be usedto supply the chilled fluid. Cool air coming from the refrigeration unit56 is connected through a pipe 58 to the opening 29 in the compartment14. In addition, the system also includes a means which is selectablyconnectable to another one of the openings for supplying a flow ofheated fluid under pressure. This means may include a blower and heatingelement combination 60. Steam could be used as the heated fluid. Inaddition, combustion gases could also furnish a heated fluid in mobileor field application of this invention. The blower and heatercombination 60 will furnish hot air through a pipe 62 to the fluid inlet24 for the compartment 12. A cross pipe 64 connects the pipe 58 to thepipe 62 through a selectively opened or closed valve 66. With the heaterand blower unit 60 turned off and the valve 66 opened, the followingaction will take place: When the blower 57 is turned on, chilled airwill be furnished from the refrigeration unit 56 through the pipe 58into the compartment 14. This chilled air will flow around the spline 22and exit to the atmosphere through the opening 28. This flow of chilledair would thereby maintain the food receptacles 40 and 41, normally inthe compartment 14 and the contents of the food receptacles 40 and 41 ina chilled state. Similarly, the chilled air will also be transferredthrough the pipe 64 and the open valve 66 into the pipe 62 which willallow the chilled air to circulate through the compartment 12 around thespline 20 and exiting to the atmosphere through the opening 25. Thiswould similarly keep the food receptacles 38 and 39, which would be inthe compartment 12, and their contents in a chilled condition. When itis desired to heat that portion of the meal which is to be served hot,the valve 66 is closed. It must be kept in mind, of course, that in thisparticular example it is the receptacles 38 and 39 and their contentswhich are to be rethermalized or heated for serving, but, of course, thesystem could be connected in a precisely opposite manner and thereceptacles 40 and 41 could contain those components of the meal whichare to be rethermalized. In this case, of course, the relative positionsof the refrigeration unit 56 and the heater and blower unit 60 wouldhave to be reversed. With the valve 66 closed, the heater and blowerunit 60 may be turned on. With the heater and blower unit 60 inoperation, heated air, or heated fluid, will be conducted into thecompartment 12 where it will flow around the spline portion 20 and exitto the atmosphere through the opening 25. This flow of heated air wouldthen heat the food receptacles 38 and 39 and the contents of these foodreceptacles. Simultaneously with this heating or rethermalizing of thatportion of the meal contained in the food receptacles 38 and 39, theflow of chilled air is maintained to the compartment 14 therebymaintaining the food receptacles 40 and 41 and their contents in achilled or cooled condition. Of course the exhaust of the heated orchilled air to the atmosphere is a relatively wasteful method ofoperating such a system, and in a large scale commercial system wouldnot be used. In a commercial system, the heated or chilled air would berecirculated through the heating or refrigeration unit and thus suchunits could be operated at maximum efficiency.

FIG. 6 is a time versus temperature chart of one specific example of theoperation of a food service tray 50 constructed in conformance with theteachings of the present invention. In the particular example given, thefood receptacles 38 and 39 respectively contained a beef patty withmushroom gravy and a potato pancake. The food receptacle 40 containedchilled, solidified, flavored gelatin and the food receptacle 41 wasempty. At the time designated as zero, all of the components within thefood tray 50 were held at a temperature of approximately 45° F. At thattime, the valve 66 was closed and the heater and blower unit 60 wasactivated. As is seen, the temperature of the air from the heater andblower unit 60 rapidly rose to a value of approximately 195° F. Thistemperature was maintained substantially constant throughout the entiretest period. The potato pancake and the meat and gravy had thermocouplesinserted at both the bottom and the top of these meal components. As isevident from the graph of FIG. 6, the two components to be served heatedrapidly reached a serving temperature of approximately 150° within aperiod of approximately 70 minutes. The gelatin contained in the foodreceptacle 40 also had a thermocouple inserted therein. As is alsoevident from the graph of FIG. 6, the gelatin was maintained at thetemperature of 45° F., in fact, even dropping somewhat in temperature toa finishing value of around 40° F. while the components of the foodreceptacle 38 and 39 were heated to the 150° temperature range. Thisexample illustrates very clearly that chilled or cooled components of ameal may be maintained in this condition while heated components may beraised to serving temperature while these components are separated by avery short distance made up of a thermally insulating material. Thisexperiment was repeated with the air temperature raised to approximately205° F., and the temperature curves were very similar to those shown inFIG. 6, with the major difference being that the hot food reachedminimum serving temperatures in about 50 minutes instead of the 70minutes as shown in FIG. 6. The gelatin was still maintained in itschilled and solidified condition. It has also been found that thecompletely frozen meal elements may be heated to serving temperatureusing the present invention. In this case, the heating time has beenfound to be about twice the time required to heat meal portions from the45° F. range to serving temperature.

I claim:
 1. A food service tray which comprises, in combination:a. abase member made of a thermally insulating material, said base memberincluding a plurality of compartments, having upstanding wall portions,open at their upper sides, each compartment having a means locatedtherein for dividing said compartment into two substantially isolated,serially connected, flow chambers, each compartment further including afluid inlet opening in one of said flow chambers and a fluid outletopening in the other one of said flow chambers; b. a plurality of foodreceptacles engaged in said plurality of compartments, said foodreceptacles being made of a thermally conductive material; and c.thermally insulating lid means for covering said plurality of foodreceptacles.
 2. The food service tray of claim 1 wherein said means fordividing said compartments comprises a spline portion extending from oneupstanding wall portion toward an opposite upstanding wall portion andterminating short of said opposite upstanding wall portion.
 3. The foodservice tray of claim 2 wherein said spline portions and said foodreceptacles are relatively proportioned to be in touching relationshipwhen said food receptacles are engaged in said base member.